it is actually a real simple matter of doing a scratch test with a pocket knife, chances are the right stone (Turquoise, Phosphate mineral) will scratch because it is under a hardness of 6 on the Mohs scale and the center 5 stones will not scratch (Silicated Chrysocolla, Chalcedony, Quartz minerals) because they are 7 on the Mohs scale and the furthest left stone (Amazonite, Feldspar mineral) is above 7 in hardness so it won't scratch either. There is much more that tell me I'm right on these stones, the surface, the colors etc........the Turquoise has the dull surface you would expect from an older piece while the copper impregnated Chalcedony/Quartz stones still appear glassy and shiny and the Feldspar has a shinier surface also, I rule out glass as well, I have cut many grams of all the materials and I am very familiar with them, I realize this is one man's opinion but it is based on many years of actually working with all the types shown.